The present invention relates to a heat treatment process for disinfection of seeds from pathogens as well as other non-desirable fungi and bacteria. The process is applicable to seeds of crops from forestry, horticulture and agriculture and is particularly applicable to seed of different crops used in agriculture and horticulture. The invention will be further described below with reference to application of the heat treatment process to cereal seed, but the invention is not restricted to said application.
Seed-borne pathogens, e.g. pathogenic fungi in cereals, every year cause great economic losses, they reduce the crop yield, deteriorate its quality and make storage of e.g. potatoe more difficult. For ecological cultivators, it is very essential that the seed is free from pathogens since control is difficult to effect during the cultivation season. The need for an ecological disinfection method against seed-borne pathogens is therefore very great. Each year large quantities of cereals are treated chemically (more than 90% of autumn-sown grain; about 40-50% of spring-sown grain) against seed-borne fungal diseases, in order to achieve a healthier crop which, owing to that, needs less or no chemical control during the cultivation season. Most cultivators are aiming at reducing the use of chemical agents for economic, environmental and working-health reasons. Therefore, there is a great need for replacing a great part of the chemical seed treatment methods by a disinfection method that does not require chemicals.
In the 1950""s and 1960""s hot water treatment was used as disinfection method in order to control loose smut in barley and wheat. The treatment was as follows (Persson, 1990):
The seed was soaked in water for about 3 hours.
It was picked up and was allowed to drain.
The wheat was placed in water of 53xc2x0 C. and the barley in water of 51xc2x0 C., for 5 minutes.
The seed was transferred to cold water for cooling, for 5 minutes.
The seed was dried.
The stated disinfection method was labour-intensive and was driven out of competition by new chemical seed treatment agents, mainly for two reasons. On one hand, the known hot water treatment method gave an uncertain effect and, on the other hand, it was costly because, above all, it was expensive to dry the seed after the treatment.
Experiments with hot water treatment of cereal seed has shown good effect against loose smut (Ustilago nuda), leaf stripe (Drechslera graminea), and net blotch (Drechslera teres) on barley, loose smut (Ustilago tritici), snow mould (Microdochium nivale), leaf and glume blotch (Stagonospora nodorum), and yellow leaf spot (Drechslera tritici-repentis) on wheat, loose smut (Ustilago avenae) and leaf stripe (Drechslera avenae) on oats as well as snow mould on rye (Bergman, 1993, 1994, 1996a, 1996b). However, in this study a great problem has been the high costs for drying the kernels after the treatment; the moisture content may be above 50% after the treatment. The cereal kernels have to be dried down to a moisture content below 15% in order for them to be stored without deterioration.
In order to avoid the costs for drying of the seed after hot water treatment, also dry hot air has been tested, however with poor results. Microwave treatment has also been tested, but without success. The explanation for this may be that, by treatment with microwaves, heat is generated inside the seed where the sensitive embryo is localized while most pathogens are on the surface of the kernel where less heat is generated. Water steam has also been tested in experiments but the high temperature gives a narrow band between the effect on pathogens and a harmful effect on the germination.
As regards the prior art, reference is also made to DD 217407, DD 297333, EP 0196464, EP 0622085, GB 1535926, GB 2150803, FR 1260436, JP 58111667, SU 422368, SU 760905 and U.S. Pat. No. 4,633,611.
The general purpose of the invention is to provide an economically interesting disinfection method in order to reduce the presence of seed-borne pathogens, with as small risk as possible for the environment; this is done in order to reduce the use of chemical controlling agents while maintaining good production possibilities.
Another purpose is to disinfect seeds by means of a carefully controlled heating without permitting changes in moisture content.
The purposes of the invention are achieved by a heat treatment process for disinfection of seeds from pathogens as well as other non-desirable fungi and bacteria, the process being characterized by supplying to the seeds non-water-borne heat while regulating the treatment time and temperature, with regard to the condition and moisture content of the seeds, in such a way that the seeds are heated from outside and in, while evaporation of moisture from the surface of the seed and, owing to that, cooling of the same is prevented. According to one embodiment of the invention, the heat supply is accomplished by contact transfer of heat to the seeds enclosed on a band conveyor, and according to a preferred embodiment the heat supply is accomplished by hot air having an air moisture content that prevents a decrease or increase of the moisture content of the seeds.
The seeds are e.g. kernels of cereals and potatoes.
By xe2x80x9cseedxe2x80x9d is herein meant the reproductive body of the seed-plants. By xe2x80x9ckernelsxe2x80x9d is herein meant seed-kernels as regards cereals, i.e. the fruits of the cereals, and seed potatoes as regards potatoe.